1. Field of the Invention
The present invention relates to a driving force-transmitting device of which main clutch is engaged by a cam mechanism amplifying torque through a pilot clutch. Concretely, the driving force-transmitting device is a coupling which distributes driving force to front and rear wheels of an all wheel drive vehicle, or is used for a limited slip differential gear which limits differential rotation between front and rear or right and left wheels of a vehicle.
2. Description of the Related Art
Heretofore, there has been known a driving force-transmitting device for an all wheel drive vehicle such as disclosed in U.S. Patent Application Publication 2002/0079178 A1 corresponding to Japanese Patent Laid Open 2002-188656. The driving force-transmitting device includes a cuplike housing, an inner shaft, a main clutch, a pilot clutch and a cam mechanism. The inner shaft is rotatably bore by the housing in a cylindrical room formed therebetween. In the cylindrical room, there are alternately arranged plural main outer and inner clutch disks of the main clutch. The main outer clutch disks are spline-engaged with the interior circumferential surface of the housing, to be non-rotatable but axially movable relative to the housing. The main inner clutch disks are spline-engaged with the exterior circumferential surface of the inner shaft, to be non-rotatable but axially movable relative to the inner shaft. Next to the main clutch in the cylindrical room, there is arranged the cam mechanism made from a first and second cam members. The second cam member is spline-engaged with the exterior circumferential surface of the inner shaft, to be non-rotatable but axially movable relative to the inner shaft. The first cam member is engaged with the second cam member, to be rotatable and axially movable relative to the second cam member. Between the first cam member and the housing, there are alternately arranged plural pilot outer and inner clutch disks of the pilot clutch. The pilot outer clutch disks are spline-engaged with the interior circumferential surface of the housing, to be non-rotatable but axially movable relative to the housing. The pilot inner clutch disks are spline-engaged with the first cam member, to be non-rotatable but axially movable relative to the first cam member. In such driving force-transmitting device, when pilot torque at the pilot clutch occurs, the cam mechanism generates relative rotational and axial movement between the first and the second cam members. Thus the main clutch is pressurized by the second cam member and transmits torque between the housing and the inner shaft, to be amplified by the cam mechanism.
In the above mentioned driving force-transmitting device, as shown in FIG. 1, the pilot inner clutch disks 101 of the pilot clutch 100 are spline-engaged with the first cam member 102, and the second cam member 104 is spline-engaged with the inner shaft 103 by spline grooves R. When an electromagnet, not shown, generates magnetic force and attracts an armature 105, the pilot torque is transmitted through the pilot clutch 100 from the housing 106 to the first cam member 102. Because of each of the spline-engagements, there occurs the cam action of relative rotational and axial movement between the first and the second cam members 102 and 104. For the cam action, the bottomed spline grooves R are formed on the second cam member 104 in order to engage the inner shaft 103.
However, where the bottomed spline grooves R are formed by cold forging or form rolling, there is formed an incomplete groove portion at each bottom of the spline groove R, so that the incomplete groove portions may bite the inner shaft 103 on the spline grooves. Therefore, the incomplete groove portions should be machined and eliminated after the spline grooves R are formed, or a concavity should be formed at a part of each bottom of the spline groove R, so that there increases the production process of the second cam member 104. There is another method to simultaneously form the second cam member 104 and the spline grooves R by sintering, however sintering costs. Further, the second cam member 104 becomes larger because the spline grooves R exist.